As one of causes of noise generation in a pneumatic tire, there is cavity resonance resulting from vibration of air filled inside the tire. This cavity resonance is generated because, when the tire is rotated, the tread portion of the tire vibrates due to irregularities on a road surface, and consequently, the vibration of the tread portion vibrates air inside the tire.
As a method of reducing noise resulting from a cavity resonance phenomenon as described above, there has been proposed one where a sound absorbent is added inside the tire to absorb the cavity resonance (for example, refer to Patent Document 1). However, in the above method, the sound absorbent is pasted to an inner surface of the tire, or to an outer peripheral surface of a rim. Therefore, the above method is disadvantageous in that installation work of the sound absorbent is troublesome.
Additionally, in the above method, while cavity resonance is suppressed by the sound absorbent, noise generated inside a tire when a vehicle is traveling is not limited to the cavity resonance, but includes high-frequency noise and the like in frequency bands different from that of the cavity resonance. However, although the sound absorbent has excellent sound absorption characteristics with respect to a particular frequency band, it does not necessarily have sufficient sound absorption characteristics with respect to other frequency bands. Therefore, even though it is possible to reduce the cavity resonance, it is difficult to reduce high-frequency noise and the like.
[Patent Document 1] Japanese patent application Kokai publication No. Sho64-78902